The present invention relates to electric machines, such as motors or generators, and more particularly to a three-phase electric machine having aluminum windings.
Electric machines, such as motors or generators, typically include a stator mounted inside a housing and a rotor supported in the housing to rotate relative to the stator. The stator and/or the rotor of the machines have windings comprising coils of wire. In motors, electricity is delivered through these coils to generate magnetic fields, causing the rotor to turn. In generators, the electricity is generated in the windings as the rotor turns. Although different electrically conductive materials may be used to make the windings, in the past these windings have frequently been made from copper or copper alloys.
Three-phase systems are used to power large motors and other large electrical loads. Three-phase electric motors are a common class of three-phase loads. Three-phase induction motors are often used to drive scroll compressors for their efficiency, cost effectiveness and durability. Scroll compressors are desirable in devices such as air conditioners for their efficiency in compressing gas refrigerant.
The size, performance and cost of the apparatus incorporating the electric machine may be important factors when making purchasing decisions, especially for air conditioners. Additionally, the size, performance and cost of the electric machine frequently has a significant impact on the size and cost of the overall apparatus.
Prices of conductive materials used to make windings fluctuate. At times, some winding materials are more expensive than others. For example, sometimes copper is very expensive relative to other electrically conductive materials such as aluminum. Electrical conductivity of the material is also an important consideration. As conductivity decreases, larger windings must be used to overcome losses. However, larger windings raise concerns about machine size and resulting apparatus size. Thus, even though some materials such as aluminum can have a cost advantage over more frequently used materials such as copper, copper may still be used due to these other concerns such as size. Conventionally, modifying a motor designed to use copper windings so it had aluminum windings but maintained similar performance characteristics required a motor having a greater volume. This volume increase was often accomplished by substantially increasing the diameter and/or the length of the motor to accommodate increased aluminum winding volume over the conventional copper winding volume. But if the exterior size of the motor is restricted by the application in which the motor is to be used, these increases in length and/or diameter may not work, so the alternative winding material (e.g., aluminum) cannot be used without sacrificing performance. It would be advantageous if a three-phase electric machine could incorporate more cost effective materials (e.g., aluminum windings) but maintain similar performance characteristics in the motor without substantially increasing its diameter and/or length.